The large preview window allows you to zoom in on posts quickly and at their original size.
If the photo or video is too large to fit on your display, it is scaled to fit appropriately.
The large preview window can be moved to any screen and position, and is saved for future use.
To view a large preview:
Long-press on any post, shared photo or video, or activity preview.
Use the Post > Large Preview menu bar item when selecting a post via keyboard navigation or viewing the details of a post.
Post > Large Preview
When hovering your mouse cursor over a post, use the Spacebar hover shortcut.